Supplemental Disclosure to Statements of Cash Flows Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 30,380	$ 11,882	$ 36,535	$ 43,642
Restricted cash	9,366	13,803	10,680	12,383
Cash and cash equivalents and restricted cash	$ 39,746	$ 25,685	$ 47,215	$ 56,025